I use GarageBand too, and there is no way to set the sample rate manually. Garageband do it automatically. In early Versions of GB i was able to select between two choices, one for faster playback for tracking and a slower one for editing. Today GB does everything on its own.
With, i think, nearly every other DAW, incl. Logic you can select the sample rate you want. I use reaper and sometimes cubase elements ai for old projects. but i don´t like the workflow with cubase at all. And you can select any sample rate, and even you can manually adjust latency correction, because i had heavy problems with the steinberg/ yamaha USB driver and since i deleted it and run my UR22 MK2 with the osx included core audio driver, i only had to adjust the latency correction a bit but even got a little bit better, shorter latency with the core driver and no problems anymore.
On the other hand, the automatic settings with GarageBand are O.K. for me and what i´m using GB for. When i try to record something in a busy session and my very old iMac is to slow to get a decent latency to work with, i disable some “cpu hungry” plug ins, ore even lock up, (freeze) some tracks with heavy cpu load and get a better performance. Sometimes after disabling plugIns, or freezing tracks but with the latency to high, it can help to save the project and restart Garage Band, so GB seems to adjust for a quicker latency and cleaning up some unused caches, or something like this. You can even try to restart your mac. So its a bit, try and hope.
But with my old iMac Garage Band allow me running projects with enough tracks, effects and plugins for me. Its very good optimized for the mac, and especially if you use the included PlugIns. Some of them have a very dull and plane GUI with not all functions like logic, but they a technical on the same page and really good and have enough functions most of the time. Try the compressors, the reverberation section and so on.
I hope you´ll understand what i was trying to say!
Greetings and happy christmas